Coating compositions suitable for use with an overcoated photoresist

ABSTRACT

Organic coating compositions, particularly antireflective coating compositions, are provided that can be developed with an aqueous alkaline developer, including in a single step during development of an overcoated photoresist layer. Preferred coating compositions comprise a tetrapolymer that comprises at least four distinct functional groups.

This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/207,201, filed Feb. 8, 2009.

The present invention relates to compositions (including antireflective coating compositions or “ARCs”) that can reduce reflection of exposing radiation from a substrate back into an overcoated photoresist layer and/or function as a planarizing or via-fill layer. More particularly, the invention relates to organic coating compositions, particularly antireflective coating compositions, that can be developed with an aqueous alkaline developer, including in a single step during development of an overcoated photoresist layer.

Photoresists are photosensitive films used for the transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.

A major use of photoresists is in semiconductor manufacture where an object is to convert a highly polished semiconductor slice, such as silicon or gallium arsenide, into a complex matrix of electron conducting paths, preferably of micron or submicron geometry, that perform circuit functions. Proper photoresist processing is a key to attaining this object. While there is a strong interdependency among the various photoresist processing steps, exposure is believed to be one of the most important steps in attaining high resolution photoresist images.

Reflection of activating radiation used to expose a photoresist often poses limits on resolution of the image patterned in the photoresist layer. Reflection of radiation from the substrate/photoresist interface can produce spatial variations in the radiation intensity in the photoresist, resulting in non-uniform photoresist linewidth upon development. Radiation also can scatter from the substrate/photoresist interface into regions of the photoresist where exposure is not intended, again resulting in linewidth variations. The amount of scattering and reflection will typically vary from region to region, resulting in further linewidth non-uniformity. Variations in substrate topography also can give rise to resolution-limiting problems.

One approach used to reduce the problem of reflected radiation has been the use of a radiation absorbing layer interposed between the substrate surface and the photoresist coating layer.

While current organic antireflective coating compositions are highly effective for many applications, it is also frequently desired to have particular antireflective compositions to meet specific processing requirements. For instance, it may be desired to remove a crosslinked antireflective layer that has been bared of overcoated photoresist (e.g. with a positive resist, exposed resist areas removed by alkaline aqueous developer) by means other than a plasma etchant. See U.S. Pat. No. 6,844,131 and U.S. Patent Publication US20050181299. Such approaches offer the potential of avoiding additional processing steps and pitfalls associated with plasma etchant removal of a bottom antireflective coating layer.

It would be desirable to have new compositions that could be used as underlying antireflective coating layer in the manufacture of microelectronic wafers. It would be particularly desirable to have new compositions that could be used as underlying antireflective coating layer and could be removed with an aqueous photoresist developer.

We have now discovered new coating compositions that are particularly useful as underlying antireflective coating layers for an overcoated photoresist layer.

Significantly, preferred processed coating compositions of the invention may be removed to expose an underlying surface with an aqueous alkaline developer used for development of an overcoated photoresist layer. This offers a number of notable advantages, including reducing the additional processing step and costs required with use of a plasma etchant to remove the underlying coating layer.

More particularly, in a first aspect, the invention provides compositions that contain a component (sometimes referred to herein as “reaction component”) that comprises multiple, distinct functional groups.

Generally preferred reaction components are tetrapolymers (four distinct repeat units) that comprise at least four distinct functional groups. In a preferred aspect, the reaction component (tetrapolymer) comprises at least four distinct functional groups that can impart the following properties (1) dissolution rate inhibition; (2) strip resistance; (3) desired aqueous alkaline developer solubility (e.g. a photoacid-labile group such as a photoacid-labile ester (e.g. —C(═O)OC(CH₃)₃) or an acetal moiety); and (4) a chromophore group to absorb undesired reflections of photoresist exposure radiation (e.g. a carbocyclic aryl group such as optionally substituted phenyl, naphthyl or anthracenyl).

Coating compositions of the invention also may optionally contain one or more other materials in addition to the reaction component. For example, a coating composition of the invention may contain an additional component that comprises chromophore groups that can absorb undesired radiation used to expose the overcoated resist layer from reflecting back into the resist layer. Such chromophore groups may be present in a variety of composition components including the reaction component itself or an additional component may comprise chromophore groups such as an added resin which may have chromophore groups as backbone members or as pendant groups, and/or an added small molecule (e.g. MW less than about 1000 or 500) that contains one or more chromophore moieties.

Generally preferred chromophores for inclusion in coating composition of the invention particularly those used for antireflective applications include both single ring and multiple ring aromatic groups such as optionally substituted phenyl, optionally substituted naphthyl, optionally substituted anthracenyl, optionally substituted phenanthracenyl, optionally substituted quinolinyl, and the like. Particularly preferred chromophores may vary with the radiation employed to expose an overcoated resist layer. More specifically, for exposure of an overcoated resist at 248 nm, optionally substituted anthracene and optionally substituted naphthyl are preferred chromophores of the antireflective composition. For exposure of an overcoated resist at 193 nm, optionally substituted phenyl and optionally substituted naphthyl are particularly preferred chromophores.

Coating compositions of the invention also may optionally comprise an acid or acid generator compound (e.g. photoacid generator and/or thermal acid generator) to facilitate reaction of composition component(s) during lithographic thermal processing of an applied composition coating layer. A photoacid generator compound (i.e. a compound that can generate acid upon exposure to activating radiation such as 193 nm) and/or thermal acid generator compound (i.e. a compound that can generate acid upon thermal treatment) is generally suitable.

Photoacid generator compound(s) included in an underlying coating composition can generate acid upon treatment with radiation used to expose an overcoated photoresist layer. By such use of photoacid generator compound(s), acid is not liberated from the photoacid generator compound(s) prior to application of a photoresist layer over the underlying coating composition. Exposure of the applied resist layer to patterned activating radiation liberates acid from the coating composition photoacid generator compound(s) and can enhance resolution of the resist image patterned over the coating composition layer by compensating for photoacid at the resist/coating composition that may diffuse from the resist into the coating composition as well as facilitate desired selective development of the underlying coating composition during treatment with an aqueous alkaline developer.

A coating composition may be provided by an admixture of a reaction component and one or more optional components as discussed above in a solvent component. The solvent component suitably may be one or more organic solvents such as one or more alcohol solvents e.g. ethyl lactate, propylene glycol methyl ether (1-methoxy-2-propanol), methyl-2-hydroxyisobutyrate, and the like, and/or one more non-hydroxy solvents such as ethyl ethoxy propionate, propylene glycol methyl ether acetate (1-methoxy-2-propanol acetate), and the like.

The coating composition is then applied such as by spin-coating (i.e. a spin-on composition) to a substrate such as a microelectronic semiconductor wafer. The solvent carrier may be removed by heating, e.g. 170° C. to 250° C. on a vacuum hotplate.

A variety of photoresists may be used in combination (i.e. overcoated) with a coating composition of the invention. Preferred photoresists for use with the antireflective compositions of the invention are chemically-amplified resists, especially positive-acting photoresists that contain one or more photoacid generator compounds and a resin component that contains units that undergo a deblocking or cleavage reaction in the presence of photogenerated acid, such as photoacid-labile ester, acetal, ketal or ether units. Preferred photoresists for use with a coating composition of the invention may be imaged with relatively short-wavelength radiation, e.g. radiation having a wavelength of less than 300 nm or less than 260 nm such as about 248 nm, or radiation having a wavelength of less than about 200 nm, such as 193 nm or 157 nm.

The invention further provides methods for forming a photoresist relief image and novel articles of manufacture comprising substrates (such as a microelectronic wafer substrate) coated with an antireflective composition of the invention alone or in combination with a photoresist composition.

As discussed above, a processed underlying coating composition layer may be removed with the same aqueous, alkaline developer solution used to develop an overcoated photoresist layer, i.e. both the exposed photoresist layer and underlying coating composition can be removed in a single step with an aqueous alkaline developer in those regions defined by the photomask during exposure.

Thus, more particularly, preferred methods of the invention may include:

1. Applying a coating layer of a composition that comprises one or more reaction components as discussed above. The composition coating layer may be applied over a variety of substrates including a microelectronic wafer;

2. Preferably thermally treating the applied composition coating layer. The thermal treatment can remove casting solvent of the coating composition and render that composition layer substantially insoluble in photoresist casting solvents such as ethyl lactate, propylene glycol methyl ether acetate, 2-heptanone, and the like;

3. Applying a photoresist composition coating layer over the cured underlying composition coating layer. The applied photoresist layer is exposed to activating radiation such as radiation having a wavelength of below 300 nm such as 248 nm, or below 200 nm such as 193 nm, typically through a photomask to form a patterned image in the resist layer. The exposed photoresist may be thermally treated as needed to enhance or form the latent image;

4. The exposed photoresist layer is then treated with a developer solution, such as an aqueous, alkaline developer solution. The developer solution can remove the image defined in the resist layer as well as matching region of the underlying coating composition layer, i.e. where a relief image is defined through both the photoresist layer and the underlying coating composition layer.

In preferred aspects an underlying coating composition of the invention is used in combination with a positive-acting photoresist, e.g. as may be imaged at sub-300 nm and sub-200 nm wavelengths such as 248 nm or 193 nm. Chemically-amplified positive resists are preferred, which contain a component that has moieties that will undergo a deblocking or cleavage reaction in the presence of photogenerated acid, such as photoacid-labile esters or acetals. Preferred positive-acting photoresists for sub-300 nm imaging such as 248 nm comprise a polymer that comprises phenolic units and acid-labile esters and/or acetal moieties and a photoacid generator compound. Preferred positive-acting photoresists for use at sub-200 nm imaging such as 193 nm imaging are substantially free of aromatic groups, particularly resins that contain phenyl or other aromatic substitution.

In another aspect, the invention also includes methods for producing a coating composition of the invention, and methods for forming a photoresist relief image and methods for manufacturing an electronic device such as a processed microelectronic wafer.

Other aspects of the invention are disclosed infra.

As discussed above, we now provide new organic coating compositions that are particularly useful with an overcoated photoresist layer. Preferred coating compositions of the invention may be applied by spin-coating (spin-on compositions) and formulated as a solvent composition. The coating compositions of the invention are especially useful as antireflective compositions for an overcoated photoresist.

Underlying Coating Compositions

Organic coating compositions of the invention comprise one or more tetrapolymer reaction components and wherein regions of a layer of coating composition can be selectively removed with an aqueous alkaline developer composition (e.g. 0.26N tetramethyl ammonium hydroxide aqueous developer solution). Preferred reaction components are polymers with multiple, distinct functional groups.

Preferred tetrapolymer reaction components of an underlying coating composition comprise one or more photoacid-labile group which can undergo a cleavage or deprotection reaction to provide functional group(s) which promote aqueous alkaline-developer solubility, such as carboxy, fluorinated alcohol and other such moieties. Upon image-wise exposure and post-exposure bake of an overcoated photoresist layer, the photoacid-labile groups of the reaction component(s) of the underlying coating composition can react and liberate functional group(s) which promote aqueous alkaline-developer solubility.

As discussed above, preferably, a tetrapolymer reaction component of an underlying coating composition contains other functional groups in addition to acid labile groups, such as chromophore groups; solvent strip resistance groups (decreases the rate of dissolution of the reaction component in carrier solvent (s) of an overcoated photoresist layer); dissolution rate promoters (do not contain photoacid-labile groups but nevertheless can promote dissolution rate in aqueous alkaline developer; acid-labile groups); and the like.

More particularly, preferred functional groups of a reaction component include the following:

1. Chromophore groups: An organic functional group with sufficient absorbance at 248 nm (KrF exposure) or 193 nm (ArF exposure) to provide for reflection control in antireflective applications. Various substituted anthracenes, naphthalenes, and phenyl groups are examples of preferred chromophores. Such chromophores may be incorporated into a polymer using the following monomers: anthracene methyl methacrylate (ANTMA), hydroxystyrene monomer (PHS), acetoxy-styrene monomer (4AS), hydroxyvinylnaphthalene monomer (HVN), and 2-Methyl-acrylic acid 6-hydroxy-naphthalen-2-ylmethyl ester (HNMA-2).

2. Solvent strip resistance groups. An organic functional group that, as a component of a polymer, decreases the rate of dissolution of the polymer in the various selected organic solvents that are commonly employed in KrF and ArF-type resist formulations. These include PGMEA, ethyl lactate and hydroxy isobutyric acid methyl ester. Solvent strip resistance groups can permit the application of an over-coated photoresist layer to the underlayer without intermixing. Various substituted imides, amides, lactones, carboxylic acids, carboxylic acid esters and other hydrolysable groups are examples of functional groups that provide some amount of solvent strip resistance to a polymer-based underlayer composition. Such solvent strip resistance promoters may be incorporated into a polymer using the following exemplary monomers: maleimide, norbornyl lactone acrylate monomer (NLA), norbornyl lactone methacrylate monomer (NLM), tert-butyl acrylate (TBA), and tert-butyl methacrylate (TBM).

3. Dissolution rate promoter groups. An organic functional group that, as a component of a polymer, promotes (increases) the rate of dissolution of the polymer in aqueous tetramethylammonium hydroxide solution (0.26N). Various substituted imides, amides, phenols, sulfonamides, fluorinated alcohols including hexafloroalcohols (e.g. —C(CF₃)₂)H), lactones, carboxylic acids, carboxylic acid esters and other hydrolysable groups are examples of preferred dissolution rate promoters. Such dissolution rate promoters may be incorporated into a polymer using the following monomers: maleimide, hydroxystyrene monomer, acetoxystyrene monomer, hydroxyvinylnaphthalene monomer (HVN), norbornyl lactone acrylate monomer (NLA), and norbornyl lactone methacrylate monomer (NLM).

4. Acid-labile groups. An organic functional group that, as a component of a polymer, may undergo an acid-catalyzed deprotection reaction. In these applications, the acid-catalyst is provided by means of a photo-acid generator (PAG), which provides acid in the exposed regions during the photolithographic processing of an over-coated photoresist. The deprotection reaction significantly increases the rate of dissolution of the polymer in developer solutions, permitting the removal of the photoresist and the underlying composition layer exposed areas with good pattern fidelity. The fast dissolution rate in aqueous developer solutions, provided by the de-protected acid labile groups, eliminates or at least minimizes any underlying coating composition residue or scumming observed in the exposed regions after development. The acid-catalyzed de-protection reaction of tert-butyl acrylate esters is a preferred example.

Preferred underlying coating compositions of the invention do not undergo significant crosslinking (molecular weight increases of composition component(s)) upon thermal treatment such as 180° C. or 240° C. for 1 to 5 minutes. See Example 7 which follows for a protocol for assessing whether a coating layer does not undergo substantial crosslinking.

Suitable molecular weights of tetrapolymers of underlying coating compositions of the invention may vary rather widely, e.g. suitably weight average molecular weights may range from about 1,000 to 50,000, more preferably about 1,500 to 10,000, 20,000 or 30,000.

Exemplary preferred tetrapolymer reaction components and syntheses thereof for use in the present underlying coating compositions are set forth in the examples which follow.

As discussed above, particularly preferred underlying coating compositions of the invention additionally may comprise one or more photoacid generator compounds. Activation of the photoacid generator compound(s) during image-wise exposure of an overcoated photoresist layer can result in reaction of acid-labile groups of the reaction component(s) of the underlying coating composition and enable subsequent one-step development of both the imaged photoresist and underlying coating composition layers.

A wide variety of photoacid generator compounds may be employed in an underlying coating compositions including ionic and compounds e.g. onium salts (such as sulfonium and/or iodonium compounds), and non-ionic photoacid generators such as imidosulfonates, N-sulfonyloxyimides, disulfone compounds, and nitrobenzyl-based photoacid generators, and other photoacid generators that have been used in photoresist compositions. Specifically suitable photoacid generator compounds for use in the present coating compositions include those identified below for use in photoresist compositions as well as the ionic and non-ionic photoacid generators disclosed in U.S. Pat. Nos. 6,20,911 and 6,803,169, such as sulfonium compounds including triphenyl sulfonium salts, iodonium compounds including diphenyl iodonium compounds and imidosulfonates and other non-ionic photoacid generator compounds. Other particularly suitable photoacid generator compounds for use in the present underlying photoresist compositions include N-[(perfluorooctanesulfonyl)oxy]-5-norbornene-2,3-dicarboximide.

One or more photoacid generators may be employed in an underlying coating composition in a variety of amounts, e.g. where the one or more photoacid generator compounds are present in amounts of about 5 weight percent or less based on total solids (all components except solvent carrier) of an underlying coating composition, suitably less than 4, 3, 2 or even 1 weight percent of total solids of an underlying coating composition.

Another optional additive of underlying coating compositions of invention, particularly when one or more photoacid generator compound (s are present in such composition is an added base, e.g. tetrabutylammonium hydroxide (TBAH), or tetrabutylammonium lactate, or a hindered amine such as diazabicyclo undecene or diazabicyclononene. The added base is suitably used in relatively small amounts, e.g. about 0.03 to 5 percent by weight relative to the total solids of the underlying coating composition.

Coating compositions of the invention, particularly for reflection control applications, also may contain additional dye compounds that absorb radiation used to expose an overcoated photoresist layer. Other optional additives include surface leveling agents, for example, the leveling agent available under the tradename Silwet 7604 from Union Carbide, or the surfactant FC 171 or FC 431 available from the 3M Company or PolyFox PF-656 from Omnaova.

As discussed above, a coating composition of the invention is suitably formulated as a liquid spin-on composition and contain one or more blended solvents. Suitable solvents include e.g. a lactate such as ethyl lactate or methyl acetate, an acetate such as amyl acetate, one or more of the glycol ethers such as 2-methoxyethyl ether (diglyme), ethylene glycol monomethyl ether, and propylene glycol monomethyl ether; solvents that have both ether and hydroxy moieties such as methyl-2-hydroxyisobutyrate, methoxy butanol, ethoxy butanol, methoxy propanol, and ethoxy propanol; esters such as methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate and other solvents such as dibasic esters, propylene carbonate and gamma-butyro lactone, ketones such as heptanone (particularly 2-heptanone) and cyclohexanone, and the like.

To make a liquid coating composition of the invention, the component(s) of the coating composition are dissolved in a suitable solvent such as, for example, one or more of ethyl lactate, propylene glycol methyl ester acetate, and/or methyl-2-hydroxyisobutyrate. The preferred concentration of the dry component(s) in the solvent will depend on several factors such as the method of application. In general, the solids content of a coating composition varies from about 0.5 to 20 weight percent of the total weight of the coating composition, preferably the solids content varies from about 2 to 10 weight of the coating composition. Of the total solids (all materials except solvent carrier) of an underlaying coating composition, the reaction product component (e.g. one or more resins) may comprises the majority of the weight of total solids of the composition, e.g. where 60, 70, 80, 90, 95 or more weight percent of a coating composition is comprised of the reaction product component. See the examples which follow for exemplary preferred amounts of materials of underlying coating compositions of the invention.

Photoresist Compositions

A variety of photoresist compositions can be employed with coating compositions of the invention, including positive-acting and negative-acting photoacid-generating compositions, as discussed above. Photoresists used with coating compositions of the invention typically comprise a resin and a photoactive component, typically a photoacid generator compound. Preferably the photoresist resin binder has functional groups that impart alkaline aqueous developability to the imaged resist composition.

As discussed above, particularly preferred photoresists for use with coating compositions of the invention include chemically-amplified resists, including positive-acting chemically-amplified resist compositions, where the photoactivated acid in the resist layer induces a deprotection-type reaction of one or more composition components to thereby provide solubility differentials between exposed and unexposed regions of the resist coating layer. A number of chemically-amplified resist compositions have been described, e.g., in U.S. Pat. Nos. 4,968,581; 4,883,740; 4,810,613; 4,491,628 and 5,492,793, all of which are incorporated herein by reference for their teaching of making and using chemically amplified positive-acting resists.

Coating compositions of the invention also may be used with other positive resists, including those that contain resin binders that comprise polar functional groups such as hydroxyl or carboxylate and the resin is used in a resist composition in an amount sufficient to render the resist developable with an aqueous alkaline solution. Generally preferred resist resins are phenolic resins including phenol aldehyde condensates known in the art as novolak resins, homo and copolymers or alkenyl phenols and homo and copolymers of N-hydroxyphenyl-maleimides as well as copolymers of fluorinated alcohols including hexafluoroalcohols (e.g. —C(CH₃)₂OH).

Preferred positive-acting photoresists for use with an underlying coating composition of the invention contains an imaging-effective amount of photoacid generator compounds and one or more resins that are selected from the group of:

1) a phenolic resin that contains acid-labile groups that can provide a chemically amplified positive resist particularly suitable for imaging at 248 nm. Particularly preferred resins of this class include: i) polymers that contain polymerized units of a vinyl phenol and an alkyl acrylate, where the polymerized alkyl acrylate units can undergo a deblocking reaction in the presence of photoacid. Exemplary alkyl acrylates that can undergo a photoacid-induced deblocking reaction include e.g. t-butyl acrylate, t-butyl methacrylate, methyladamantyl acrylate, methyl adamantyl methacrylate, and other non-cyclic alkyl and alicyclic acrylates that can undergo a photoacid-induced reaction, such as polymers in U.S. Pat. Nos. 6,042,997 and 5,492,793, incorporated herein by reference; ii) polymers that contain polymerized units of a vinyl phenol, an optionally substituted vinyl phenyl (e.g. styrene) that does not contain a hydroxy or carboxy ring substituent, and an alkyl acrylate such as those deblocking groups described with polymers i) above, such as polymers described in U.S. Pat. No. 6,042,997, incorporated herein by reference; iii) polymers that contain repeat units that comprise an acetal or ketal moiety that will react with photoacid, and optionally aromatic repeat units such as phenyl or phenolic groups; such polymers have been described in U.S. Pat. Nos. 5,929,176 and 6,090,526, incorporated herein by reference; (iv) polymers that comprise t-butoxycarbonyl oxy protecting (tBoc) groups; and (v) polymer blends wherein at least one polymer of the blend comprises acid-labile group;

2) a resin that is substantially or completely free of phenyl or other aromatic groups that can provide a chemically amplified positive resist particularly suitable for imaging at sub-200 nm wavelengths such as 193 nm. Particularly preferred resins of this class include: i) polymers that contain polymerized units of a non-aromatic cyclic olefin (endocyclic double bond) such as an optionally substituted norbornene, such as polymers described in U.S. Pat. Nos. 5,843,624, and 6,048,664, incorporated herein by reference; ii) polymers that contain alkyl acrylate units such as e.g. t-butyl acrylate, t-butyl methacrylate, methyladamantyl acrylate, methyl adamantyl methacrylate, and other non-cyclic alkyl and alicyclic acrylates; such polymers have been described in U.S. Pat. No. 6,057,083; European Published Applications EP01008913A1 and EP00930542A1; and U.S. pending patent application Ser. No. 09/143,462, all incorporated herein by reference, and polymers that contain polymerized anhydride units, particularly polymerized maleic anhydride and/or itaconic anhydride units, such as disclosed in European Published Application EP01008913A1 and U.S. Pat. No. 6,048,662, both incorporated herein by reference.

3) a resin that contains repeat units that contain a hetero atom, particularly oxygen and/or sulfur (but other than an anhydride, i.e. the unit does not contain a keto ring atom), and preferable are substantially or completely free of any aromatic units. Preferably, the heteroalicyclic unit is fused to the resin backbone, and further preferred is where the resin comprises a fused carbon alicyclic unit such as provided by polymerization of a norborene group and/or an anhydride unit such as provided by polymerization of a maleic anhydride or itaconic anhydride. Such resins are disclosed in PCT/US01/14914 and U.S. Pat. No. 6,306,554.

4) a resin that contains fluorine substitution (fluoropolymer), e.g. as may be provided by polymerization of tetrafluoroethylene, a fluorinated aromatic group such as fluoro-styrene compound, and the like. Examples of such resins are disclosed e.g. in PCT/US99/21912.

Suitable photoacid generators to employ in a photoresist coated over or above a coating composition of the invention include imidosulfonates such as compounds of the following formula:

wherein R is camphor, adamantane, alkyl (e.g. C₁₋₁₂ alkyl) and perfluoroalkyl such as perfluoro(C₁₋₁₂alkyl), particularly perfluorooctanesulfonate, perfluorononanesulfonate and the like. A specifically preferred PAG is N-[(perfluorooctanesulfonyl)oxy]-5-norbornene-2,3-dicarboximide.

Sulfonate compounds are also suitable PAGs for resists overcoated a coating composition of the invention, particularly sulfonate salts. Two suitable agents for 193 nm and 248 nm imaging are the following PAGS 1 and 2:

Other known photoacid generator compounds also may be employed in the resists of the invention, such as other onium salts including those disclosed in U.S. Pat. Nos. 4,442,197, 4,603,101, and 4,624,912, as well as non-ionic organic photoactive compounds such as the halogenated photoactive compounds as in U.S. Pat. No. 5,128,232 to Thackeray et al. Additional suitable photoacid generators for use in photoresists employed with coating compositions of the invention include sulfonate photoacid generators including sulfonated esters and sulfonyloxy ketones. See J. of Photopolymer Science and Technology, 4(3):337-340 (1991), for disclosure of suitable sulfonate PAGS, including benzoin tosylate, t-butylphenyl alpha-(p-toluenesulfonyloxy)-acetate and t-butyl alpha(p-toluenesulfonyloxy)-acetate. Preferred sulfonate PAGs are also disclosed in U.S. Pat. No. 5,344,742 to Sinta et al.

Photoresists for used with an underlying coating composition of the invention also may contain other materials.

A preferred optional additive of photoresists overcoated a coating composition of the invention is an added base, particularly tetrabutylammonium hydroxide (TBAH), or tetrabutylammonium lactate, which can enhance resolution of a developed resist relief image. For resists imaged at 193 nm, a preferred added base is a hindered amine such as diazabicyclo undecene or diazabicyclononene. The added base is suitably used in relatively small amounts, e.g. about 0.03 to 5 percent by weight relative to the total solids.

Other optional photoresist additives include actinic and contrast dyes, anti-striation agents, plasticizers, speed enhancers, etc. Such optional additives typically will be present in minor concentration in a photoresist composition except for fillers and dyes which may be present in relatively large concentrations such as, e.g., in amounts of from about 5 to 50 percent by weight of the total weight of a resist's dry components.

Various substituents and materials (including reaction components and reagents to form same, resins, small molecule compounds, acid generators, etc.) as being “optionally substituted” may be suitably substituted at one or more available positions by e.g. halogen (F, Cl, Br, I); nitro; hydroxy; amino; alkyl such as C₁₋₈ alkyl; alkenyl such as C₂₋₈ alkenyl; alkylamino such as C₁₋₈ alkylamino; carbocyclic aryl such as phenyl, naphthyl, anthracenyl, etc; and the like.

Lithographic Processing

As discussed above, in use, a coating composition of the invention is applied as a coating layer to a substrate by any of a variety of methods such as spin coating. The coating composition in general is applied on a substrate with a dried layer thickness of between about 0.02 and 0.5 μm, preferably a dried layer thickness of between about 0.04 and 0.20 μm. The substrate is suitably any substrate used in processes involving photoresists. For example, the substrate can be silicon, silicon dioxide or aluminum-aluminum oxide microelectronic wafers. Gallium arsenide, silicon carbide, ceramic, quartz or copper substrates may also be employed. Substrates for liquid crystal display or other flat panel display applications are also suitably employed, for example glass substrates, indium tin oxide coated substrates and the like. Substrates for optical and optical-electronic devices (e.g. waveguides) also can be employed.

As discussed preferably the applied coating layer is treated (e.g. thermal treatment) to remove solvent carrier (but without significant molecular weight increases of composition component(s)) before a photoresist composition is applied over the composition layer. Thermal treatment conditions can vary with the components of the coating composition, particularly if the coating composition contains an acid or acid source such as a thermal acid generator. Suitable thermal treatment cure conditions may range from about 140° C. to 250° C. for about 0.5 to 30 minutes. Thermal conditions preferably render the coating composition coating layer substantially insoluble to solvent carrier of the overcoated photoresist composition to avoid any significant intermixing of the respective two coating layers.

After treatment of the coating composition layer, a photoresist is applied over the surface of the coating composition. As with application of the bottom coating composition, the overcoated photoresist can be applied by any standard means such as by spinning, dipping, meniscus or roller coating. Following application, the photoresist coating layer is typically dried by heating to remove solvent preferably until the resist layer is tack free.

The resist layer is then imaged with activating radiation through a mask in a conventional manner. The exposure energy is sufficient to effectively activate the photoactive component of the resist system to produce a patterned image in the resist coating layer. Typically, the exposure energy ranges from about 3 to 300 mJ/cm² and depending in part upon the exposure tool and the particular resist and resist processing that is employed. The exposed resist layer may be subjected to a post-exposure bake if desired to create or enhance solubility differences between exposed and unexposed regions of a coating layer. For example, negative acid-hardening photoresists typically require post-exposure heating to induce the acid-promoted crosslinking reaction, and many chemically amplified positive-acting resists require post-exposure heating to induce an acid-promoted deprotection reaction. Typically post-exposure bake conditions include temperatures of about 50° C. or greater, more specifically a temperature in the range of from about 50° C. to about 160° C.

The exposed resist coating layer is then developed, preferably with an aqueous based developer such as an alkali exemplified by tetra butyl ammonium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium silicate, sodium metasilicate, aqueous ammonia or the like. In general, development is in accordance with art recognized procedures, except that development will also result in removal of the underlying coating composition layer in those areas underlying resist layer regions removed by the developer. Preferably, development will be terminated (e.g. by spin-drying and/or water rinse) once development of the image transferred from the resist layer is complete in the underlying coating layer to avoid excessive and undesired removal of the underlying, e.g. removal of the composition coating layer is areas where the resist layer is retained after difficult. Optimal development times to avoid either under-development or over-development of the underlying coating composition layer can be readily determined empirically with any particular system of resist, underlying composition, developer composition and development conditions, e.g. the development can be conducted for varying times prior to termination as discussed above, and the developed images evaluated such as by scanning electron micrographs (SEMs) to determine development times or time ranges where over-development or under-development does not occur.

Following development, a final bake of an acid-hardening photoresist is often employed at temperatures of from about 100° C. to about 150° C. for several minutes to further cure the developed exposed coating layer areas.

The developed substrate may then be selectively processed on those substrate areas bared of photoresist and the underlying coating composition layer, for example, chemically etching or plating substrate areas bared of photoresist in accordance with procedures well known in the art. Suitable etchants include a hydrofluoric acid etching solution and a plasma gas etch such as an oxygen plasma etch. Notably, an additional step of plasma removal of the underlying composition layer is not required where removal is accomplished in the same step as photoresist layer development, as discussed above.

All documents mentioned herein are incorporated herein by reference in their entirety. The following non-limiting examples are illustrative of the invention.

Example 1 Synthesis of MI/ANTMA/HNMA-2/TBA 34.3/31.5/25.0/9.2 tetrapolymer

Into a 2.0 L, 5-necked round bottom flask, fitted with a mechanical stirrer, condenser, heating mantle, and temperature controller, were added 215 g dioxane. The solvent was sparged with nitrogen gas for 15 minutes. The solvent was heated to 85° C.

Into a 2.0 L Erlenmeyer flask with stir bar were added maleimide (MI, 53.10 g, 547 mmol), 9-anthracene-methyl methacrylate (ANTMA, 138.7 g, 502 mmol), 2-hydroxynaphthalene-methylmethacrylate monomer (HNMA-2, 96.53 g, 398 mmol), t-butyl acrylate (TBA, 18.80 g, 147 mmol) and dioxane (423.5 g). The mixture was allowed to stir at room temperature for 30 minutes. The solution was sparged with nitrogen gas for 15 minutes.

Into a 500 mL bottle were added 2,2-azobis(2,4-dimethylvaleronitrile (Vazo® 52, 11.89 g, 48.0 mmol) and dioxane (78.0 g).

The monomer solution was fed to the reaction flask with a peristaltic pump over 1.5 hours at a rate of 8.5 g/min. The initiator solution was also fed to the reaction flask with a peristaltic pump over this period at a rate of 1.1 g/min (90 min feed).

Upon completion of the monomer and initiator feed, a solution of 2,2-azobis(2,4-dimethylvaleronitrile (Vazo® 52, 7.93 g, 32.0 mmol) and dioxane (151 g) was fed to the reaction flask with a peristaltic pump over 20 minutes at a rate of 8.0 g/min.

When complete, the reaction mixture was held at 85° C. for 1.5 hours.

After cooling to room temperature, the reaction mixture was precipitated into 15.0 L of methanol. The white precipitate was isolated by vacuum filtration, washed with 3.0 L of methanol and dried in a vacuum oven overnight at 50° C.

195.1 g (64%) of the title polymer was obtained as a white powder. GPC (THF) M_(w)=9300 Da, M_(n)=6500 Da, PDI: 1.5.

Example 2 Synthesis of MI/ANTMA/HNMA-2/TBA 33.2/31.3/26.8/8.7 tetrapolymer

Into a 2.0 L, 5-necked round bottom flask, fitted with a mechanical stirrer, condenser, heating mantle, and temperature controller, were added 218 g dioxane. The solvent was sparged with nitrogen gas for 15 minutes. The solvent was heated to 85° C.

Into a 2.0 L Erlenmeyer flask with stir bar were added maleimide (MI, 51.39 g, 529 mmol), 9-anthracene-methyl methacrylate (ANTMA, 137.9 g, 499 mmol), 2-hydroxynaphthalene-methylmethacrylate monomer (HNMA-2, 103.4 g, 427 mmol), t-butyl acrylate (TBA, 17.82 g, 139 mmol) and dioxane (430 g). The mixture was allowed to stir at room temperature for 30 minutes. The solution was sparged with nitrogen gas for 15 minutes.

Into a 500 mL bottle were added 2,2-azobis(2,4-dimethylvaleronitrile (Vazo® 52, 11.89 g, 48.0 mmol) and dioxane (78.0 g).

The monomer solution was fed to the reaction flask with a peristaltic pump over 1.5 hours at a rate of 7.5 g/min. The initiator solution was also fed to the reaction flask with a peristaltic pump over this period at a rate of 0.9 g/min (90 min feed).

Upon completion of the monomer and initiator feed, a solution of 2,2-azobis(2,4-dimethylvaleronitrile (Vazo® 52, 7.93 g, 32.0 mmol) and dioxane (151 g) was fed to the reaction flask with a peristaltic pump over 20 minutes at a rate of 8.2 g/min.

When complete, the reaction mixture was held at 85° C. for 1.5 hours.

After cooling to room temperature, the reaction mixture was precipitated into 15.0 L of methanol. The white precipitate was isolated by vacuum filtration, washed with 3.0 L of methanol and dried in a vacuum oven overnight at 50° C.

186.6 g (60%) of the tile polymer was obtained as a white powder. GPC (THF) M_(w)=9200 Da, M_(n)=6350 Da, PDI: 1.5.

Example 3 Coating Composition Preparation and Lithographic Processing

An underlying coating composition is prepared by admixing the following materials:

Reaction Component (Resin)

Polymer of Example 1 above

Photoacid Generator

triphenyl sulfonium salt

Solvent

ethyl lactate

The reaction component was percent in an amount of 5 grams. The photoacid generator compound is present in an amount of about 0.5 weight percent of total solids (all components expect solvent).

This formulated coating composition is spin coated onto a silicon microchip wafer and is cured at 210° C. for 60 seconds on a vacuum hotplate to provide a dried (but not cross-linked) coating layer.

A commercially available 193 nm positive-acting photoresist is then spin-coated over the cured coating composition layer. The applied resist layer is soft-baked at 100° C. for 60 seconds on a vacuum hotplate, exposed to patterned 193 nm radiation through a photomask, post-exposure baked at 110° C. for 60 seconds and then developed with 0.26 N aqueous alkaline developer where both the photoresist later and underlying coating composition are removed in areas defined by the photomask.

Example 4 Coating Composition Preparation and Lithographic Processing

An underlying coating composition is prepared by admixing the following materials:

Tetrapolymer Reaction Component

Polymer of Example 2 above

Photoacid Generator

triphenyl sulfonium salt

Solvent

ethyl lactate

The reaction component was percent in an amount of 5 grams. The photoacid generator compound is present in an amount of about 0.5 weight percent of total solids (all components expect solvent).

This formulated coating composition is spin coated onto a silicon microchip wafer and is cured at 210° C. for 60 seconds on a vacuum hotplate to provide a dried (but not cross-linked) coating layer.

A commercially available 193 nm positive-acting photoresist is then spin-coated over the cured coating composition layer. The applied resist layer is soft-baked at 100° C. for 60 seconds on a vacuum hotplate, exposed to patterned 193 nm radiation through a photomask, post-exposure baked at 110° C. for 60 seconds and then developed with 0.26 N aqueous alkaline developer where both the photoresist later and underlying coating composition are removed in areas defined by the photomask.

Example 5 Coating Composition Preparation and Lithographic Processing

An underlying coating composition is prepared by admixing the following materials:

Tetrapolymer Reaction Component

Polymer Blend of Examples 1 and 2 above

Photoacid Generator

triphenyl sulfonium salt

Solvent

ethyl lactate

The reaction component was percent in an amount of 5 grams. The photoacid generator compound is present in an amount of about 0.5 weight percent of total solids (all components expect solvent).

This formulated coating composition is spin coated onto a silicon microchip wafer and is cured at 210° C. for 60 seconds on a vacuum hotplate to provide a dried (but not cross-linked) coating layer.

A commercially available 193 nm positive-acting photoresist is then spin-coated over the cured coating composition layer. The applied resist layer is soft-baked at 100° C. for 60 seconds on a vacuum hotplate, exposed to patterned 193 nm radiation through a photomask, post-exposure baked at 110° C. for 60 seconds and then developed with 0.26 N aqueous alkaline developer where both the photoresist later and underlying coating composition are removed in areas defined by the photomask.

Example 6 Coating Composition and Lithographic Processing

A coating composition was prepared by admixing the following components: materials:

Tetrapolymer Reaction Component

Polymer Blend of Examples 1 and 2 above

Photoacid Generator

triphenyl sulfonium salt

Solvent

methyl 2-hydroxyisobutyrate

In this coating come coating composition, the reaction component (resin) is present in an amount of 3.2 grams, the acid source (thermal acid generator) is present at about 0.8 weight percent of total solids and an photoacid generator is present at about 2% weight percent of total solids (all materials except solvent). The solvent is present in an amount of about 96 weight percent of the total coating composition weight.

This coating composition is spin coated onto a silicon wafer substrate and baked at 215° C. to remove solvent, but does not result in crosslinking of the coating composition layer.

A 193 nm photoresist composition is spin-coated over the coating composition and regions of the photoresist composition were exposed to 193 nm radiation at varying energy doses. The exposed photoresist layer is then post-exposure baked at about 110° C. for 60 seconds and the baked photoresist layers are developed with 0.26N tetramethyl ammonium hydroxide (TMAH) aqueous alkaline developer where both the photoresist later and underlying coating composition are removed in areas defined by the photomask.

Example 7 Test to Confirm that Thermal Treatment of an Underlying Coating Composition does not Result in Crosslinking (Molecular Weight Increase of Composition Components)

A solution of a polymer containing polymerized units of maleimide, polyhydroxystyrene and 9-anthracene-methyl methacrylate were spin cast onto 8″ silicon wafers and baked at 180° C. and 240° C. An unbaked coating of each material was also prepared. Formulations containing the same polymer but also a photoacid generator compound were also prepared and coatings were made on 8″ silicon wafers at the same bake temperatures (room temperature, 180° C. and 240° C.). After processing as described above, all of the coated films were scraped, readily dissolved in THF and molecular weight measured by GPC.

The weight-average molecular weight data for the polymer films with and without PAG showed minimal change after thermal processing thus indicating that crosslinking did not take place upon the thermal treatments.

The foregoing description of this invention is merely illustrative thereof, and it is understood that variations and modifications can be made without departing from the spirit or scope of the invention as set forth in the following claims. 

What is claimed is:
 1. An antireflective composition for use with an overcoated photoresist layer, comprising: a tetrapolymer that comprises polymizerized units of maleimide, 9-anthracene-methyl methacrylate, 2-hydroxynaphthalene-methylmethacrylate, and t-butyl acrylate.
 2. The composition of claim 1 wherein the coating composition further comprises an acid or acid generator compound.
 3. The composition of claim 1 wherein the coating composition further comprises a photoacid generator compound.
 4. A method for forming a photoresist relief image comprising: (a) applying over a substrate a coating layer of antireflective composition of claim 1; and (b) applying a photoresist layer above the coating composition layer.
 5. The method of claim 4 wherein the coating composition further comprises an acid or acid generator compound.
 6. The method of claim 4 wherein the coating composition further comprises a photoacid generator compound.
 7. The method of claim 4 wherein the antireflective coating composition layer is not crosslinked at the time the photoresist layer is applied.
 8. The method of claim 4 wherein the applied photoresist layer is exposed to patterned radiation and then developed with an aqueous alkaline developer composition, whereby the developer composition selectively removes in both the photoresist layer and the underlying coating composition layer the image as defined in the photoresist layer by patterned radiation. 